$\dfrac{1}{100} + \dfrac{2}{10} = {?}$
Answer: The fractions must have the same denominator before you can add them. Rewrite $\dfrac{2}{10}$ as $\dfrac{20}{100}$ $\dfrac{1}{100} + \dfrac{20}{100} = {?}$ $ = \dfrac{21}{100}$